scholarly journals Dependence of Thermal Shock Crack on Specimen Width for Ceramic Materials

2016 ◽  
Vol 08 (03) ◽  
pp. 1650042
Author(s):  
Xianghong Xu ◽  
Wenjun Yuan ◽  
Cheng Tian
Keyword(s):  
Size Effect ◽  
Thermal Shock ◽  
Crack Depth ◽  
Ceramic Materials ◽  
Elastic Strip ◽  
Modified Model ◽  
Specimen Width ◽  
Proposed Model ◽  
Theoretical Results ◽  
Good Agreement

Knowledge of size effect of thermal shock properties of ceramics is a prerequisite in engineering applications. In the present study, the size effect of the cracking in the ceramic materials subjected to water quenching has been experimentally conducted. Based on the Rizk model, the equivalent specimen width of the elastic strip with cracks is introduced and modified to describe the effect of cracks on the deformation of the elastic strip underwater quenching. It is found that the simulation obtained from the proposed modified model is in good agreement with the experimental results. And the reasons for the size effect of crack depth and crack growth into the compressive region are well analyzed by theoretical results. The proposed model is expected to provide a powerful tool to characterize and predict the size effect on thermal shock crack of ceramic materials.

Chaos Induced Transition

1997 ◽  
Vol 07 (04) ◽  
pp. 855-867 ◽  
Author(s):  
Toshihiro Shimizu ◽  
Nozomi Morioka
Keyword(s):  
Stationary Distribution ◽  
Logistic Map ◽  
Period Doubling ◽  
Bifurcation Parameter ◽  
Proposed Model ◽  
Linear Harmonic Oscillator ◽  
Small Change ◽  
Intermittent Chaos ◽  
Theoretical Results ◽  
Good Agreement

To study the coherent nature of chaos, two models are proposed. Model 1 is a simple nonlinear system [Formula: see text] and Model 2 is a linear harmonic oscillator [Formula: see text], which are driven by a chaotic force f(t). The chaotic force f(t) is defined by [Formula: see text] for nτ < t ≤ (n + 1)τ(n = 0, 1, 2, …), where yn+1 is a chaotic sequence of a map F(y; r) with the bifurcation parameter r: yn+1 = F(yn; r) (-0.5 ≤ yn ≤ 0.5) and ŷn = yn - < y0>. In Model 1 the relaxation process of this system and the τ- and r-dependence of the stationary distribution of x are discussed. It is shown that the small change of the bifurcation parameter r causes the drastic change of the stationary distribution. In Model 2, resonance phenomena are investigated near the period 3 window of the logistic map, in particular, in the intermittent chaos region and the period doubling region. The theoretical results are shown to be in a good agreement with numerical ones, which have been done for the logistic map as F(y; r).

Estimation of Thermal Shock Resistance by Infrared Radiation Heating and Water Flow Cooling Techniques

2006 ◽  
Vol 317-318 ◽  
pp. 339-342
Author(s):  
Sawao Honda ◽  
Hiroaki Tanaka ◽  
Hideo Awaji
Keyword(s):  
Thermal Shock ◽  
Thermal Shock Resistance ◽  
Rapid Heating ◽  
Ceramic Materials ◽  
Shock Resistance ◽  
Testing Techniques ◽  
Experimental Values ◽  
Definition Of ◽  
Increasing Temperature ◽  
Good Agreement

Thermal shock is a mechanism often leading to failure of ceramic materials that may occur during rapid heating or cooling. These tests were performed in order to compare the thermal shock resistance of ceramic materials by cooling with that of the heating method and hence to evaluate parameters such as thermal shock strength (R1c) and thermal shock fracture toughness (R2c). During the present study, thermal shock resistance of alumina and mullite ceramics was estimated experimentally and theoretically using the thermal shock parameters. The critical thermal stress at the onset of thermal shock fracture was calculated using fracture time, which is measured by an acoustic emission. Results show that thermal shock parameters of alumina specimens decreased with increasing temperature of fracture point. This effect can be attributed to the temperature dependence of the thermal properties. The experimental values of thermal shock parameters evaluated by IRH and WFC techniques were in good agreement at the temperature of fracture point. The thermal shock parameters enabled the definition of a unified thermal shock resistance of ceramics, which is independent of the nature of the testing techniques.

Analysis of snake rolling force and torque with changes of thickness depending on unequal roll radii based on pure aluminum experiments

2016 ◽  
Vol 231 (1) ◽  
pp. 161-174 ◽  
Author(s):  
HY Wang ◽  
ZH Wang ◽  
DH Zhang ◽  
DW Zhao
Keyword(s):  
Rolling Force ◽  
Pure Aluminum ◽  
Speed Ratio ◽  
Roll Speed ◽  
Equivalent Radius ◽  
Roll Torque ◽  
Offset Distance ◽  
Proposed Model ◽  
Theoretical Results ◽  
Good Agreement

An analytical model, in which unequal radii are replaced with an equivalent radius, is creatively proposed to predict the rolling force and roll torque in general case of snake rolling. With the model, the effects of roll radius ratio, roll speed ratio, offset distance between rolls, reduction and friction coefficient on rolling forces in hot snake rolling of aluminum alloy are obtained. Also, the thicknesses of slab are investigated in different zones, which firstly propose the changes of thickness during snake rolling. Owing to the good agreement with the results measured in experiments and calculated by finite element method and other traditional models, those calculated by the proposed model are verified. The proposed model can be used to predict more accurate theoretical results for snake rolling force and torque.

scholarly journals Modified Numerical Modeling of Axially Loaded Concrete-Filled Steel Circular-Tube Columns

2021 ◽  
Vol 11 (3) ◽  
pp. 7094-7099
Author(s):  
P. C. Nguyen ◽  
D. D. Pham ◽  
T. T. Tran ◽  
T. Nghia-Nguyen
Keyword(s):  
Circular Tube ◽  
Experimental Tests ◽  
Element Model ◽  
Modified Model ◽  
Proposed Model ◽  
Wide Range ◽  
Strain Relationship ◽  
Concrete Damaged Plasticity ◽  
Cfst Columns ◽  
Good Agreement

Predicting the behavior of concrete in a Concrete-Filled Steel Tubular (CFST) column is challenging due to the sensitivity to input parameters such as the size of the cross-section, the material modeling, and the boundary conditions. The present paper proposes a new modified finite element model to predict the behavior and strength of a CFST subjected to axial compression. The development is based on the concrete damaged plasticity model, with its stress-strain relationship revised from the available model. The predicted accuracy of the modified model is verified via a wide range of experimental tests. The proposed model has more accuracy than the available models in predicting the ultimate compression strength. The results show good agreement with the test data, allowing its use in modeling CFST columns.

A Stress-Strain Model for Unconfined in Compression Considering the Size Effect

2018 ◽  
Author(s):  
Keun-Hyeok Yang ◽  
Yongjei Lee ◽  
Ju-Hyun Mun
Keyword(s):  
Compressive Strength ◽  
Aspect Ratio ◽  
Size Effect ◽  
Maximum Stress ◽  
Damage Zone ◽  
Peak Stress ◽  
Specimen Width ◽  
Proposed Model ◽  
Compressive Strength Of Concrete ◽  
Strain Model

In this study, the model proposed by Yang et al. to generalize the stress&ndash;strain model for unconfined concrete with consideration of the size effect is expanded. Sim et al.&rsquo;s compressive strength model that is based on the function of specimen width and aspect ratio was used for the maximum stress. In addition, a strain at the maximum stress was formulated as a function of compressive strength by considering the size effect using the regression analysis of datasets compiled from a wide variety of specimens. The descending branch after the peak stress was formulated with consideration of less dissipated area of fracture energy with the increase in specimen width and aspect ratio in the compression damage zone (CDZ) model. The key parameter for the slope of the descending branch was formulated as a function of specimen width and aspect ratio, concrete density, and compressive strength of concrete considering the size effect. Consequently, a rational stress&ndash;strain model for unconfined concrete was proposed. This model explains the trends of the peak stress and strain at the peak stress to decrease and the slope of the descending branch to increase, as the specimen width and aspect ratio increase. The proposed model agrees well with the test results, irrespective of the compressive strength of concrete, concrete type, specimen width and aspect ratio. In particular, the proposed model for the stress&ndash;strain curve rationally considered the effect of decreasing peak stress and increasing the descending branch slope, with the increase in specimen width and aspect ratio.

An Investigation on the Diffusion of Momentum and Mass of Fuel in a Diesel Fuel Spray

1977 ◽  
Vol 99 (2) ◽  
pp. 225-235 ◽  
Author(s):  
C. M. Vara Prasad ◽  
Subir Kar
Keyword(s):  
Diesel Fuel ◽  
Injection Pressure ◽  
Ambient Air ◽  
Fuel Spray ◽  
Modified Model ◽  
Free Jet ◽  
Normal Probability ◽  
Proposed Model ◽  
Normal Probability Distribution ◽  
Good Agreement

An investigation on the diesel fuel spray injected into stagnant ambient air in a chamber is reported in this paper. The objective of the investigation was to analyze the processes of diffusion of mass and velocity of the fuel in the fuel spray. The distribution of velocity and mass of the fuel showed similarity in the zone of established flow. Gaussian normal probability distribution for free jet was assumed by earlier workers, starting with Albertson, et al., for analyzing such a situation. However, it has been found that diesel fuel spray in a chamber necessitates modification of the model described and a modified model has been proposed herein. The Abramovich model is also compared with the experimental data. The ratio of εm/εm0 varied from 1.24 to 1.45 for the change of injection pressure from 100 to 200 atm. It is conclusively shown that mass diffuses faster than the momentum, the rate of diffusion increasing with the increase in the injection pressure. The proposed model gives good agreement with experimental results. The various parameters of the equations for depicting the fuel spray as a jet have been evaluated and tabulated.

Investigating the Nonlinear Optical Response of Pepper Oil under Low Power Irradiation with Continuous Wave Visible Laser Beam

2020 ◽  
pp. 131-138
Keyword(s):  
Refractive Index ◽  
Nonlinear Refractive Index ◽  
Nonlinear Optical ◽  
Continuous Wave ◽  
Diffraction Integral ◽  
Visible Laser ◽  
Limiting Property ◽  
Kirchhoff Diffraction Integral ◽  
Theoretical Results ◽  
Good Agreement

The nonlinear optical properties of pepper oil are studied by diffraction ring patterns and Z-scan techniques with continuous wave beam from solid state laser at 473 nm wavelength. The nonlinear refractive index of the sample is calculated by both techniques. The sample show high nonlinear refractive index. Based on Fresnel-Kirchhoff diffraction integral, the far-field intensity distributions of ring patterns have been calculated. It is found that the experimental results are in good agreement with the theoretical results. Also the optical limiting property of pepper oil is reported. The results obtained in this study prove that the pepper oil has applications in nonlinear optical devices.

scholarly journals Phase Transition and Coefficients of Thermal Expansion in Al2−xInxW3O12 (0.2 ≤ x ≤ 1)

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4021
Author(s):  
Andrés Esteban Cerón Cerón Cortés ◽  
Anja Dosen ◽  
Victoria L. Blair ◽  
Michel B. Johnson ◽  
Mary Anne White ◽  
...  
Keyword(s):  
Phase Transition ◽  
Thermal Expansion ◽  
Thermal Shock ◽  
Monoclinic Phase ◽  
Ceramic Materials ◽  
Precipitation Method ◽  
Scanning Calorimetry ◽  
Orthorhombic Crystal ◽  
Co Precipitation

Materials from theA2M3O12 family are known for their extensive chemical versatility while preserving the polyhedral-corner-shared orthorhombic crystal system, as well as for their consequent unusual thermal expansion, varying from negative and near-zero to slightly positive. The rarest are near-zero thermal expansion materials, which are of paramount importance in thermal shock resistance applications. Ceramic materials with chemistry Al2−xInxW3O12 (x = 0.2–1.0) were synthesized using a modified reverse-strike co-precipitation method and prepared into solid specimens using traditional ceramic sintering. The resulting materials were characterized by X-ray powder diffraction (ambient and in situ high temperatures), differential scanning calorimetry and dilatometry to delineate thermal expansion, phase transitions and crystal structures. It was found that the x = 0.2 composition had the lowest thermal expansion, 1.88 × 10−6 K−1, which was still higher than the end member Al2W3O12 for the chemical series. Furthermore, the AlInW3O12 was monoclinic phase at room temperature and transformed to the orthorhombic form at ca. 200 °C, in contrast with previous reports. Interestingly, the x = 0.2, x = 0.4 and x = 0.7 materials did not exhibit the expected orthorhombic-to-monoclinic phase transition as observed for the other compositions, and hence did not follow the expected Vegard-like relationship associated with the electronegativity rule. Overall, compositions within the Al2−xInxW3O12 family should not be considered candidates for high thermal shock applications that would require near-zero thermal expansion properties.

scholarly journals Compact Modelling of Electrical, Optical and Thermal Properties of Multi-Colour Power LEDs Operating on a Common PCB

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1286
Author(s):  
Krzysztof Górecki ◽  
Przemysław Ptak
Keyword(s):  
Integrated Circuits ◽  
Optical Model ◽  
Printed Circuit Board ◽  
Circuit Board ◽  
Junction Temperature ◽  
Optical Parameters ◽  
Spice Simulation ◽  
Light Emitting ◽  
Proposed Model ◽  
Good Agreement

This paper concerns the problem of modelling electrical, thermal and optical properties of multi-colour power light-emitting diodes (LEDs) situated on a common PCB (Printed Circuit Board). A new form of electro-thermo-optical model of such power LEDs is proposed in the form of a subcircuit for SPICE (Simulation Program with Integrated Circuits Emphasis). With the use of this model, the currents and voltages of the considered devices, their junction temperature and selected radiometric parameters can be calculated, taking into account self-heating phenomena in each LED and mutual thermal couplings between each pair of the considered devices. The form of the formulated model is described, and a manner of parameter estimation is also proposed. The correctness and usefulness of the proposed model are verified experimentally for six power LEDs emitting light of different colours and mounted on an experimental PCB prepared by the producer of the investigated devices. Verification was performed for the investigated diodes operating alone and together. Good agreement between the results of measurements and computations was obtained. It was also proved that the main thermal and optical parameters of the investigated LEDs depend on a dominant wavelength of the emitted light.

Studies of local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) crystals

2021 ◽  
Vol 76 (4) ◽  
pp. 299-304
Author(s):  
Fu Chen ◽  
Jian-Rong Yang ◽  
Zi-Fa Zhou
Keyword(s):  
Crystal Field ◽  
Elongation Ratio ◽  
Paramagnetic Resonance ◽  
Local Structures ◽  
Epr Parameters ◽  
Structure Constants ◽  
Crystal Field Parameters ◽  
Electron Paramagnetic ◽  
Theoretical Results ◽  
Good Agreement

Abstract The electron paramagnetic resonance (EPR) parameters (g factor g i , and hyperfine structure constants A i , with i = x, y, z) and local structures for Cu2+ centers in M2Zn(SO4)2·6H2O (M = NH4 and Rb) are theoretically investigated using the high order perturbation formulas of these EPR parameters for a 3d 9 ion under orthorhombically elongated octahedra. In the calculations, contribution to these EPR parameters due to the admixture of d-orbitals in the ground state wave function of the Cu2+ ion are taken into account based on the cluster approach, and the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the studied EPR parameters with the local structures of the Cu2+ centers. Based on the calculations, the Cu–H2O bonds are found to suffer the axial elongation ratio δ of about 3 and 2.9% along the z-axis, meanwhile, the planar bond lengths may experience variation ratio τ (≈3.8 and 1%) along x- and y-axis for Cu2+ center in (NH4)2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O, respectively. The theoretical results show good agreement with the observed values.

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